Melatonin is a natural hormone found in plants and animals. It is vital to regulating a variety of bodily functions that we rarely think about unless they go wrong. These include sleep-wake cycles, dreaming, maintaining the immune system and regulating ageing.

In humans, melatonin is made in the pineal gland, located near the centre of the brain. Its chemical form is N-acetyl-5-methoxytryptamine, and once produced it is released directly into the bloodstream.

The pineal gland produces melatonin during the night, typically in response to darkness detected by the eyes. Melatonin reduces alertness, induces drowsiness and drops the body temperature; all this helps us to drop off.

During the day, melatonin production dramatically declines so that we stay alert. This 24-hour cycle is referred to as the circadian rhythm.